1. Field of the Invention
The present invention relates generally to a method for compressing a header included in a general communication packet, and more particularly, to a method for compressing a header by RObust Header Compression (ROHC).
2. Description of the Related Art
A header compression method has been proposed to more efficiently utilize radio resources when a multimedia service is used in a wireless environment having limited available bandwidth. The transmission of essential items is provided without an invariable item in every packet transmission or a fixed value in protocol headers (Internet protocol (IP), user datagram protocol (UDP), and real-time transport protocol (RTP) headers, etc.) used for real-time multimedia service transmission. As a result of this effort, data that is to be repeatedly transmitted through a header may be reduced.
A representative header compression method is an ROHC method described in Internet Engineering Task Force (IETF) Request For Comments (RFC) 3095. According to this method, a header to be used in each protocol may be reduced remarkably. Specifically, an (IP+UDP+RTP) header basically needs 40 bytes, but may be transmitted using only an average of several bytes by removing data that is transmitted repeatedly and transmitting only specific items.
RTP has a 12-byte basic header size when used as a protocol in real-time multimedia data transmission. RTP provides a header extension in which additional information may be transmitted with the basic header. When RTP was designed, an RTP header extension was not used actively. However, there has recently been an increase in the use of the RTP header extension to provide an additional service. In an RTP standard, only a basic frame is defined, but a use method totally depends on a user. Attempts are being made to solve a problem occurring in the use of the RTP header extension. In the RTP standard, a header extension field 20 capable of transmitting additional information is provided in addition to a 12-byte basic header 10 as illustrated in FIG. 1. For use of the RTP header extension field, a specific bit provided to identify the use of the header extension field 13 (for example, x-bit as a flag indicating the use of the extension header) is set to “1”. The header extension field 20 is inserted after the RTP basic header 10. The header extension field 20 includes a 2-byte profile item (identification information) field 21, a 2-byte length item field 22, and a header extension body 23 into which actual data is inserted.
A header extension field may be used in a data packet using the ROHC method, but the extension field is not specially compressed. Accordingly, when the header extension field is used, header compression efficiency achieved by using the ROHC method may be degraded.
Use of the RTP header extension field is gradually increasing and the RTP header extension field is being used for various purposes.